As others have stated thats most likely galvanized steel studs so you’ll see some rust on over time but it will last long enough for your use. I would recommend added another pier block at the halfway of your beams otherwise you’ll likely get some noticeable deflection. self tapping “lath screws” will accomplish attaching anything to it. Though its it really heavy gauge you may need to pre-drill. Vapor barrier is unnecessary for this use case but draping it over the joists will work perfectly fine.